A lithium secondary battery (and typically, a lithium ion battery) is known that charges and discharges by migration of lithium ions between a positive electrode and a negative electrode. In a typical configuration employed by this type of lithium secondary battery, an electrode is provided that has a configuration in which a material capable of reversibly absorbing and desorbing lithium ions (active material) is retained on an electrically conductive member (current collector). At present, graphite is widely used as a negative electrode active material. In the case of graphite, however, since only one Li is intercalated per six carbon atoms, the charge-discharge capacity thereof has an upper limit of 372 mAh/g.
Therefore, various studies have been conducted on active materials expected to be able to realize a charge-discharge capacity greater than that of graphite. One example of such an active material is that having a composition that contains an iron oxide such as Fe2O3 (oxide containing iron as a constituent element). For example, Patent Document 1 describes a lithium secondary battery in which an iron oxide thin film, formed by depositing from a vapor phase or liquid phase onto a substrate, is used for the positive electrode active material. Examples of other technical documents relating to the use of iron oxide in a lithium secondary battery include Patent Documents 2 to 5.    Patent Document 1: Japanese Patent Application Laid-open No. 2002-298834    Patent Document 2: Japanese Patent Application Laid-open No. S62-219465    Patent Document 3: Japanese Patent Application Laid-open No. H11-111294    Patent Document 4: Japanese Patent Application Laid-open No. 2003-257426    Patent Document 5: Japanese Patent Application Laid-open No. H3-112070